1. Technical Field
Nitrogen is used to improve the process of stabilizing clays with an aqueous potassium hydroxide solution.
2. Background Information
Sandstone formations containing fine particles can be damaged when the fine particles come in contact with an aqueous solution containing an ionic makeup different from that of the connate waters. Such can cause permeability reduction and reduce the flow of fluids through both injection wells and production wells. It is especially prevalent in such formations where brines become progressively fresher. The "fine" particles are not limited to clays but include all swelling and potentially mobile fine particles within the sandstone pore bodies. Examples of such fine particles include clay minerals, large surface area silica (SiO.sub.2) minerals, feldspars, mica, and barite.
Encroachment of the "fresher" brines in the sandstone formation can occur in a variety of different ways. For example, invasion by an underlying aquifer, invasion of an enhanced oil recovery process, invasion of fluids used to treat near wellbore phenomenon, and like instances. Two distinct types of clay damage can result from such encroachment. First, swellable clays, such as montmorillonite having interstitial layers, swell when contacted with the fresher brines reducing the permeability to fluid flow therethrough. Secondly, migratable clays, such as poorly cemented kaolinite and illite clay particles, become detached from the sandstone formation during the flow of fresh water therethrough and the clay particles become trapped in the formation pore-throat openings reducing permeability and fluid flow therethrough. Often, encroachment of fresher brines into a sandstone formation containing clays results in the occurrence of both types of permeability damage.
To overcome this problem, U.S. Pat. No. 3,640,343 teaches injecting an aqueous solution of alkali metal silicate containing SiO.sub.2 to stabilize such formations, especially during drilling or fluid production. U.S. Pat. No. 4,536,304 teaches stabilizing fine particles in a formation by contacting the particles with nitrogen-containing cationic perfluorinated compounds. This treatment can be done in conjunction with an acidizing process. Also the art teaches the use of organic polycationic polymers to prevent or reduce the adverse effects of swelling clays or migrating fines or combinations thereof in subterranean formations. See U.S. Pat. Nos. 4,366,071; 4,366,072; 4,366,073; 4,366,074; 4,374,739; 4,460,483 and 4,462,718.
U.S. Pat. No. 4,534,413 teaches stimulating water flow in a well by injecting liquid or gaseous nitrogen and/or liquid or gaseous carbon dioxide into the well and alternately pressurizing and depressurizing the well to cause the formation between the well wall and the water supply to be exposed to high pressures and fractures to thereby stimulate the flow of water into the well.
U.S. Pat. No. 4,280,560 teaches the use of potassium hydroxide to stabilize sandstone formations containing water-sensitive fine particles. The potassium hydroxide interacts with the fine particles to substantially prevent formation permeability damage caused by encroachment of water having an ionic makeup different from the connate water. The potassium hydroxide renders the fine particles immobile.